The present invention relates generally to the generation of pseudo-random number sequences used, for example, in encryption procedures. More particularly, the present invention relates to a pseudo-random number sequence generator, and an associated method, by which to generate a pseudo-random number sequence corresponding to a sequence generated by a selected windmill polynomial. The present invention further relates to a manner by which to determine compatibility between different configurations of windmill polynomial-based pseudo-random sequence generators.
Word-oriented memory elements are used to store words which form the pseudo-random number sequence. The sizes of the memory words are selected such that sizes of sequence portions generated by the windmill generator during successive iterations of operations can be readily increased, as desired, thereby to facilitate the generation of the same pseudo-random number sequence at increased rates, corresponding to alternate, compatible windmill generator constructions.
The pseudo-random number sequence generated through operation of an embodiment of the present invention is advantageously utilized as part of a system to encrypt data to be communicated over a radio link, such as a radio link formed between a mobile terminal and a radio base station of a cellular communication system. The pseudo-random number sequence generated through operation of an embodiment of the present invention is also advantageously utilized in spread-spectrum (e.g., Code Division Multiple Access) communications, in automated ranging systems, in voice signal compression methods, and in radar systems.
A communication system is operable to communicate information between a sending station and a receiving station by way of a communication channel. In a wireline communication system, the communication channel is formed of a fixed connection between the sending and receiving stations. And, in a radio communication system, the communication channel forms a portion of the electromagnetic frequency spectrum. Because a fixed connection is not required to form the communication channel between the sending and receiving stations of a radio communication system, communications are possible when a fixed connection between the sending and receiving stations would be impractical.
A digital communication system is a communication system in which information to be communicated by a sending station to a receiving station is digitized. A digital communication system can be implemented in both a wireline communication system and a radio communication system. A digital communication system permits more efficient utilization of the communication channel extending between the sending and receiving stations, thereby permitting the communication capacity of the communication system to be increased over that of a conventional, analog communication system.
Communications between sending and receiving stations are sometimes desired to be private in nature. That is to say, parties sending and receiving the communication signals intend only for the sending and receiving parties to be able to access the informational content of the communication signals. Particularly when the communication channel is a radio communication channel of a radio communication system, privacy of the communications between the sending and receiving stations becomes problematical. As a radio channel is inherently public in nature, a communication signal transmitted upon the radio communication channel can be detected by any receiving station, within range of the communication signal, and tuned to the radio channel. An unauthorized party, for instance, is able to tune a radio receiver to the frequency of the radio channel upon which the communication signal is transmitted, thereby to receive the communication signal. Analogous security problems are also of concern in wireline communication systems in the event that an unauthorized party gains access to the wireline communication channel.
One manner by which to improve the security of communications in a communication system is to encrypt the information forming a communication signal into encrypted form. If only authorized parties are able to de-encrypt the encrypted communication signal, an unauthorized party is unable to discern the informational content of the communication signal transmitted upon the communication channel. Thereby, privacy of communications is better assured.
A digital information signal is particularly amenable to an encryption process. A digital information signal is formed of sequences of bits, and each bit, if desired, of the information signal can be encoded into encrypted form at the sending station prior to its transmission upon the communication channel. An unauthorized party, without knowledge of the manner by which the information signal is encrypted is unable to de-encrypt a receive signal to recover the informational content of the transmitted signal. Only a receiving station capable of de-encrypting the encrypted signal is able to recover the informational content of the receive signal.
Various manners are used by which to encrypt the digital information signal. A typical encryption scheme, such as that used in cellular communications, utilizes an encryption process by which the digitized bits of an information signal are combined with the bits of a pseudo-random sequence generated by a pseudo-random sequence generator. The pseudo-random sequence generator is operable in conjunction with a secret key which, in a symmetrical encryption technique, is known to the sending station and to an authorized receiving station. The secret key is used at the authorized receiving station to de-encrypt the encrypted signal received thereat, thereby to recover the informational content of the transmitted signal.
The pseudo-random number sequences are sometimes derived by the calculation of a windmill polynomial. Constructions, whether hardware or software implemented, which form pseudo-random number sequences in this manner are sometimes referred to as windmill generators. Output bits generated by a windmill generator form the pseudo-random number sequences which are used, inter alia, to encrypt an information signal. A windmill generator is directly related to a selected, primitive polynomial over some finite field GF(q). When q=2, the finite field GF(2) is referred to as the binary case and is of significance particularly in digital communications. The number of primitive polynomials from which a windmill generator can be derived is limited due to many constraints placed on the polynomial. Especially in the binary case when the polynomial is required to exhibit, to minimize processing operations needed to generate outputs therefrom, only a few non-zero coefficients, the number of suitable polynomials which can be used to form a windmill polynomial is limited. The number of non-zero coefficients of a polynomial is referred to as the weight of the polynomial.
Tables exist which list primitive polynomials, such as, for the binary case of GF(2), primitive polynomials with three or five non-zero coefficients and with degrees of up to five thousand.
The randomness of outputs, sometimes herein referred to as xe2x80x9cn-tuplesxe2x80x9d, generated by a binary windmill polynomial of weight=3 is generally poor, so to increase the randomness of the outputs, a high-weight polynomial is required. But, such improved randomness occurs at the expense of increased processing requirements. Existing tables cannot always be used to select a windmill polynomial suitable from which to derive a pseudo-random number sequence as such existing tables do not necessarily show all primitive polynomials with a selected, e.g., three or five, number of non-zero coefficients. Particularly when the pseudo-random number sequences are used for an encryption process, knowledge of all windmill polynomials of a selected degree over the finite field GF(2) is valuable. Methods are not available by which to derive such knowledge. Instead, conventionally, a searching process, including a test for primitivity, such as the Knuth Allanen test, is performed.
Vanes taken from a conventional windmill generator are determinative of the bit-size of the outputs, i.e., the n-tuples, formed by the generator. As processing capabilities improve with successive generations of processing devices operable at increased processing speeds, conventional windmill generators having greater numbers of vanes become increasingly practical. A windmill generator having increased numbers of vanes is capable of generating larger bit-sized outputs. And, hence, a pseudo-random number sequence can be more quickly generated.
When a windmill generator configuration is compatible with a windmill generator of another configuration, the same pseudo-random number sequence is generated by the generators of each configuration. Such compatibility is generally required so that apparatus and processes utilizing windmill generators of the different configurations are all capable of operation to produce the same results.
There, however, is no existing manner by which simply to determine compatibility of different configurations of windmill generators. Conventionally, compatibility between separate configurations can be realized only by mapping one initial state of one configuration to that of another configuration. But such mapping requires a significant number of operations to be performed. Special windmill polynomials, however, permit a very simple transformation between configurations.
It would, accordingly, be advantageous to provide a manner by which to determine the compatibility of alternate configurations of windmill generators by which to generate a common pseudo-random number sequence.
It would further be advantageous to provide a windmill generator of simplified construction and capable of generating pseudo-random number sequences corresponding to a selected windmill polynomial but capable of simple conversion to alternate configurations, as desired.
It is in light of this background information related to the generation of pseudo-random number sequences that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides a manner by which to determine the compatibility of alternate configurations of windmill generators by which to generate a common pseudo-random number sequence.
The present invention, accordingly, further advantageously provides a windmill generator of simplified construction and capable of generating pseudo-random number sequences corresponding to a selected windmill polynomial but capable of simple conversion to alternate configurations, as desired.
Configurations of windmill generators are identified which, when initialized to be of selected initial states, generate n-tuples which form the same pseudo-random number sequence. The identified configurations have simple relations to one another; that is to say, configurations are identified by which mere copying of initial state values in a selected relation result in operation of the different configurations generating the same pseudo-random number sequences. Such copying has a linear complexity in the dimension of a state space, i.e., the degree of the generating polynomial, and not a quadratic complexity, conventionally required to map one initial state to an equivalent other.
In one implementation, pseudo-random number sequences generated by a windmill generator of an embodiment of the present invention is used as a subcomponent to encrypt information to be transmitted by a sending station to a receiving station. In an exemplary implementation, the communication system forms a cellular communication system, and information to be communicated between a mobile terminal and network infrastructure of the cellular communication system is encrypted through the use of a pseudo-random number generated by the windmill generator. The encryption of a received, encrypted signal is analogously also performed with the utilization of the pseudo-random number sequence generated by a windmill generator, thereby to de-encrypt the encrypted signal.
In another aspect of the present invention, an efficient method is provided by which to generate efficiently consecutive blocks of pseudo-random noise sequence in particular maximum-length sequences and full-length sequences. Because a word-oriented memory implementation is utilized by which to form the pseudo-random number sequences, such sequences are generated quickly, without significant computational requirements. And, through proper selection of the memory word size, alternate configurations of windmill generators are realized to permit upward and backward compatibility of pseudo-random number sequences.
In these and other aspects, a method, and associated apparatus, generates a pseudo-random noise sequence. A set of memory elements is formed in which each memory element of the set stores a memory word of a selected word plane therein. Each of the memory elements is initialized with initial state values. The initial state values with which each of the memory elements is initialized form memory words stored therein. At least one of the memory words stored in at least one of the memory elements is selected to form an output sequence. The output sequence forms a portion of the pseudo-random noise sequence. At least one new memory word is selected to be stored in at least one of the memory elements of the set of memory elements. The new memory word is formed of selected combination of memory words stored in the memory elements of the set of memory elements. The at least one new memory word corresponds in number with the number of memory words selected to form the output sequence.
A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims.